This invention relates to a fluid-pressure-operated, double-acting work cylinder having a piston member constructed with an integral piston cushioning arrangement; more specifically, such integrally cushioned piston member being of a single-body construction. Typically, work cylinders have included multiple-component piston assemblies having a number of seals and seal-attaching means which, by requiring such a plurality of components, only serve to increase the cost of the device both at the manufacturing and maintenance levels.
Additionally, typical multiple-component piston assemblies have attempted to include a cushioning arrangement to the work piston which, by engaging a reduced-diameter chamber portion, have used a fixed amount of fluid to cause a pressure buildup acting in an opposing direction to movement of the work piston to effect a cushioning of the final piston movement. Such cushioning arrangements have had the disadvantage of requiring an additional number of components at a higher cost and, furthermore, have proven to be limited in effect, are not accurately controllable and adjustable with respect to the cushioning effect due to the trapping of the fixed amount of fluid. By cushioning with a fixed amount of trapped fluid, the sealing arrangements of the work pistons have also been unduly strained since, as the piston nears the final stopping point, the fluid pressure generated in an opposing direction to work piston movement, increases significantly thereby adversely affecting the work piston seals.
Furthermore, such piston cushioning arrangements have required an extended length of the cylinder chamber to effect cushioning and still provide a port opening such that, fluid pressure could be introduced to the chamber to move the work piston in the opposite direction. This comes about as a result of the need to have an amount of chamber space sufficient to compress the fixed amount of trapped fluid to achieve a fluid pressure level which can cushion work piston movement.
Still other work cylinder, piston assemblies have attempted to provide a single-body piston construction incorporating the seals as a part of the piston body, and further, including a type of piston cushioning thereon as well. An example of such a work cylinder piston assembly can be found in U.S. Pat. No. 2,984,529, wherein a single piston has a sealing material coating and a plurality of rubber buttons to cushion piston movement. This approach, however, has the disadvantage of cushioning mainly by contact of the buttons to a chamber portion, there being little provision for fluid pressure buildup to cushion piston movement, inasmuch as the space between the button allows escape of any fluid pressure around this cushioning arrangement.